Conventional fryers store a specified amount of cooking oil in an oil tank and heat it with a gas or electric heater. With the cooking oil heated to a set temperature, the fryer stands by and food materials are thrown in for frying. After a predetermined cooking time, the fried food is taken out and put on paper or an oil draining pan to remove excess oil. Now the frying operation is complete.
Therefore, with the conventional fryer the cooking oil remains at high temperatures continuously even when no frying operation is performed.
The conventional fryer cannot easily collect deep-fried batter balls that disperse from food ingredients into the cooking oil during the frying process, colloidal materials drifting away from the food being fried, and impurities including water, smell and fat flowing out of the food material. These unwanted materials that stay long in the cooking oil cause early degradation of the oil and darken its color, which in turn contaminate the food.
Further, since colloidal, floating oil dirt and deep-fried batter balls adhere to food and sidewalls of the oil tank, the oil must be filtered into a separate container every day to let floating substances to settle over time and the interior of the oil tank cleaned every day.
Generally, a range of temperature of the frying cooking oil agrees with a temperature range that accelerates early degradation and oxidation of oil. In the conventional fryer, it is necessary to raise a large quantity of cooking oil to a set temperature in a short time and to prevent its temperature drop during the frying process and, if dropped, recover it to the set temperature in a short time. For this reason, the heater is operated at a temperature higher than the set temperature of the cooking oil. So, the oil in contact with the surface of the heater in particular is subjected to a far higher temperature than the set temperature.
This accelerates degradation and oxidation of the cooking oil, increases oil smoke and evaporation, and rapidly changes the composition of the oil. As a result, the conventional fryer needs to replace the cooking oil frequently, giving rise to a problem of a high economic burden.
In cooking, food materials are often covered with batters or bread crumbs for frying. During frying, a large volume of batter and crumbs comes off the food, disperses into the cooking oil and is heated and carbonized. This in turn darkens the oil and over time degrades its quality. Therefore, to maintain the quality of the cooking oil, deep-fried batter balls and other discharged substances must be removed frequently. However, this removal work is difficult considering the convenience of the frying process and the construction of the fryer.
During the frying process, water in the food is replaced with the cooking oil. A large amount of water and water vapor flows out of the food into the atmosphere and the cooking oil. The water discharged into the atmosphere turns into smoke and, along with the oil, into oil mist, contaminating the interior of the kitchen and equipment. Further, the water released into the cooking oil mixes with the oil over time, contributing to oxidation and degradation of the oil.
The water that did not mix with the cooking oil after being released into the oil remains in a low-temperature oil layer between a lower part of the heater and the bottom of the oil tank. If the fryer is kept in operation for a long period of time, the oil temperature in the low-temperature oil layer increases and the water remaining at the bottom of the oil tank begins to evaporate, moving up from the low-temperature oil layer to a high-temperature cooking oil layer. As it rises, the water is further heated and continues to expand its volume until it is released into the atmosphere from an oil surface. If this process is continued, there is a risk of the oil flowing over the oil tank.
For removing fine particles of the deep-fried batter balls and lipid substances, a means is available by which the cooking oils is drawn out, removed of the deep-fried batter balls floating in the oil as by filter paper and then cleaned by a cleaner as the oil is returned to the tank. With this means, however, the water released into the oil cannot be removed sufficiently. It is also difficult to perform the cleaning each time the fryer is used.
Patent document 1: Japanese Patent Disclosure No. 55-40249
Patent document 2: Japanese Patent Disclosure No. 60-9426
Patent document 3: Japanese Patent Disclosure No. 5-68440
The above-described conventional fryer keeps the cooking oil at an elevated temperature at all times even when not in use, in order to be ready at any time to perform the frying operation. This deteriorates the cooking oil and shortens its life, leading to the frequent replacement of the oil. Furthermore, this mode of operation necessarily consumes heat energy wastefully for many hours.
Many, large and small deep-fried batter balls coming off the food are dispersed in oil layers and are difficult to remove completely with an existing removal net. It is even more difficult to remove them during the frying process. In the case of a gas type fryer, a heater is fixed and the removal net cannot be inserted under the heater. So one possible method may be to use a sucking type cleaner or another method may involve drawing out the cooking oil from under the oil tank onto a container having the removal net therein and removing the unwanted substances. This, however, takes time and is practically impossible as a means to be performed during the frying process. As a result, the deep-fried batter balls are left in the cooking oil for many hours, shortening the life of the oil.
While the food is being fried, smoke, oil mist and water vapor are released from the oil surface in large quantities. Although the volume of their release decreases when foods are not being fried, smoke and oil mist are always rising. A dedicated exhaust device installed above the fryer cannot discharge them sufficiently, leaving smell and possible environmental contaminations.
Deep-fried batter balls coming off the food, colloidal substances flowing out of it and floating in the oil, and water and smell released from the food material are spread widely into the entire oil during cooking. In addition, there are lots of fine particles of these unwanted materials. Therefore they cannot be collected quickly, which in turn shortens the life of the oil, giving rise to an economic problem. As described above, leaving the unwanted deep-fried batter balls in the hot cooking oil for many hours causes smells, smoke and oil mist to adhere to equipment and human body, polluting the environment.
The present invention has been accomplished to overcome the above-described problems and it is an object of this invention to provide a fryer capable of preventing a degradation of cooking oil, securing a good kitchen environment and enhancing a work efficiency.